BIOLOGY OF TRIARTHRIA-SETIPENNIS (FALLEN) (DIPTERA, TACHINIDAE), A NATIVE PARASITOID OF THE EUROPEAN EARWIG, FORFICULAAURICULARIA L (DERMAPTERA, FORFICULIDAE), IN EUROPE

Triarthria setipennis is a tachinid parasitoid of the European earwig (Folficula auricularia) and following introduction from Europe has bec ome established in British Columbia and Newfoundland, where it provide s low levels of control. Populations of T. setipennis were surveyed in central Europe during 1989-1991 and individual insects reared to iden tify available biotypes that may be more effective than biotypes alrea dy established in Canada. Additional information is provided on parasi toid biology; this could facilitate new introduction of T. setipennis which could be used to augment existing or introduced populations in C anada for the control of F. auricularia. Microclimatic conditions and sufficient territory space for pairs are important to elicit mating ac tivity. Older males mated readily with newly emerged females. The gest ation period of mated females is on average 19 days. Triarthria setipe nnis is ovolarviparous and lays its eggs close to potential hosts. Che micals are involved in the host-finding and host-acceptance response o f the females. Females lay on average 235 eggs. The oviposition period lasts 4-5 days. Once a first-instar larva contacted a host, it mounte d it and tried to penetrate through the intersegmental skin between th e head and thorax, or on the thorax or abdomen; this process takes les s than 3 min. Only 16.7% of the parasitoids manage to penetrate the ho st successfully. The duration of larval development is variable, takin g from 2 weeks to 2 months during June and July. Most pupae were obtai ned during August. Overwintering occurs in the pupal stage. In Germany and in the northwestern part of Switzerland there is one full and a p artial second generation per year. The first generation of T. setipenn is in southern Austria shows a long emergence period and the individua ls differ markedly in colour. The highest rate of parasitism in the fi eld was 46.9%.